Control system for preventing the overload of relay windings



L. E. EARLING Jan. 2l, 1969 CONTROL SYSTEM FOR REVENTING THE OVERLOAD OF RELAY WINDINGS United States Patent O Claims This invention relates lto a control system uti-lizing Zener diodes in circuits containing relay windings so as to render the variable efects of relay resistances, line resistances, and other circuit parameters less critical than otherwise and to avoid overloading the relay windings.

It is among the objects of this invention to provide a control system comprising a voltage source, a relay winding, a resistor, and Ia control element, all connected in a series circuit, a Zener diode connected in parallel with the relay winding, and switching means connected across at least a portion `of the resistor, whereby closure of the switching means produces an increase in voltage across the control eelment without increasing the current in the relay winding. It is also contemplated that a second relay winding be connected in the series circuit and a second Zener diode be connected in parallel with the second winding. It is also contemplated that there be a second circuit containing a voltage source, a control relay winding, and a gating device in series, Iand a Zener diode in parallel with the control element and in circuit with the gating device rendering the gating device conductive when the voltage across the control element exceeds the voltage rating of the last Zener diode. It is contemplated that this rgating device assume the form of a transistor and it is contemplated that the control element be ia resistor. This invention is eminently suited for the remote control of recorders and the relay winding under such circumstances will operate contacts for energizing and deenergizing such a recorder. The voltage source may include a plurality of Zener diodes arranged in series. The series circuit may include a microphone, the anode and cathode electrodes of a silicon control rectier and contacts controlled by the relay winding.

A more complete understanding of the invention will follow from a description of the drawing wherein:

FIG. 1 is a circuit dia-gram depicting an embodiment of the invention; and

FIG. 2 is a simplified circuit diagram, based upon FIG. l; omitting -many of the components which are not necessary for tracing the circuits primarily involved. and depicting a condition under which certain of the relays have been actuated as compared with their deenergized conditions depicted in FIG. 1.

A recording station 10 has been depicted wit-hin the broken lines of FIG. l, comprising a recorder 12, controlled by a relay 144 and supplied from a suitable power source 14, and a D.C. supply 16. The recording station provides terminals 18, 20, 22 and 24 for connection with conductors 26, 28, 30 and 32 from one or more remote dictating stations.

Each dictating station comprises a neon tube 34, a selector switch 36 having contacts 38, 40, 42, 44 `and 46, a cradle switch 48 under the inuence of a cradle 50 to receive a handset, the cradle switch having contacts 52, I54 and 56 which assume their lower positions when the handset reposes in the cradle 50. Each dictating station also includes a relay winding 58 shunted by a Zener diode 60 and having contacts 62, 64 and 66, one side of the relay winding 58 Ibeing connected in series with a resistor 68 shunted by a start-stop switch 70, and in series with a microphone 72. a resistor 74, and the anode-cathode path of a silicon controlled rectifier 76. Also as shown in FIG. 1, each dictating station includes a receiver 78.

3,423,640 Patented Jan. 21, 1969 Fice Others of the components provided at the recording and dictating stations will be referred to in the description of the operation of the system, to follow.

When the recording and dictating stations are interconnected as depicted in FIG. 1, but with the handset in its cradle 50, the movable contacts 52, 54 and 56 of the cradle actuated switch 48 will yassume their lower positions as distinguished from the upper positions which have been depicted in FIG. l. Under such conditions, the neon tube 34 will be ionized and illuminated by means of a circuit tra-ced from t-he positive tenminal of the D.C. supply 16, through conductor 82, resistor 84, conductor 86, conductor 88, relay winding 90, resistor 91, contacts 92, terminal 20, conductor 28, neon tube 34, resistor 94, conductor 26, terminal 18, conductor 96, resistor 98, conductor and to the negative terminal 102` of the D.C. supply 16. The presence of the resistor 94 in this circuit limits the current to a value below that necessary to actuate the winding 90 of the relay 13.

When the handset at the dictating station shown. or at another dictating station connected in parallel, is removed from the cradle 50, the contacts 52, 54 and 56 will assume the positions shown in FIG. l, whereupon the recording station will be in circuit with only the dictating station whose handset has been lifted. This condition is achieved by rendering conductive the -gating device in the form of the silicon controlled rectifier 76 by completion of a circuit traced from the positive terminal 80 of the D.C. supply 16, through the conductor 82, resistor 84, conductor 86, conductor 88, winding 90, resistor 91, contacts 92, terminal 20, conductor 28, neon tube 34, couductor 104, contacts 38, resistor 106, contacts 52, conductor 108, gate of `silicon controlled rectifier 7 6, cathode 112 of the silicon controlled rectifier, conductor 114, conductor 116, contacts 40, conductor 26, terminal 18, conductor 96, resistor 98, conductor 100, and to the negative terminal 102 of the D.C. source 16. Completion of this circuit is possible only if the neon tube 34 is ionized and conducting. Due to the presence of the neon tube and the resistor 106, the current will be insufficient to actuate the relay 13.

Having rendered the silicon controlled rectier conductive, another circuit will be completed, shunting the neon tube 34 and the resistor 106, traced from the positive terminal 80 of the D.C. source .16 through conductor 82, resistor 84, conductor '86, conductor 88, winding 90, resistor 91, contacts 92, terminal 20, conductor 28, contacts 42, contacts 56, conductor 118, conductor 120, winding 58, conductor 122, resistor 68, conduct-or 124, microphone 72, conductor 126. conductor 128, resistor 74, anode and cathode 112 of the silicon controlled rectifier 76, conductor 114, conductor 116, contacts 40, conductor 26, terminal 18, conductor 96, resistor 98, conductor 100, and to the negative terminal 102 of the D.C. source 16.

The current in the windings 58 and 90 is now sufficient to actuate the relays of which they form a part, closing the contacts 62, 64 and 66 under the influence of the winding S8 and the contacts 132 under the iniluence of the winding 90. These conditions have been depicted in FIG. 2, from which many of the components of FIG. 1 have been omitted in the interests of simplification. Three Zener diodes 134, 136 and 138, in series, are connected across the D.C. source `and resistor 84 to provide a voltage across their outer terminals and 142 in excess of that required to ionize the neon tube 34. When the contacts 132 are closed, the Zener diode 138 is shunted, whereupon the voltage across the terminals 140 and 142 is reduced to a value below that required to ionize the neon tube. and it therefore is extinguished and -becomes non-conductive. Similarly, all neon tubes at dictating stations connected in parallel to recording station 10 will -have their neon tubes extinguished corresponding to tube 34, so that none of them can establish a circuit with the recording station until the neon lamps are again ionized by release of the seized circuit upon restoring the removed handset to its cradle 50.

The start-stop switch 70, usually carried by the handset, is shown with its contacts open, corresponding to a deenergized condition of the relay 144 at the recording station, since the voltage drop across the resistor 98 under the circuit conditions thus far described is less than the conductance voltage of the Zener diode 146. Under this condition, there will be no appreciable current in the base circuit of the transistor 148, and accordingly, no appreciable current in the circuit including the transistor collector 150 and the winding 152 ofthe relay 144.

'Upon actuation of the start-stop switch 70 to close its contacts, a circuit can be traced from the positive terminal 80 of the D.C. source 16 through conductor 82, resistor 84, conductor 86, the parallel path provided by t-he winding 90 and Zener diode 154, resistor 91, contacts 92, terminal 20, contacts 42. conductor 156, conductor 158, contacts 66, conductor 120, the parallel path provided by the winding 58 and the Zener diode 60, conductor 122, conductor 160, contacts of switch 70, microphone 72, conductor 126, conductor 128, resistor 74, anode 130 land cathode 112 of silicon controlled rectifier 76, conductor 114, conductor 116, Icontacts 40, conductor 26, terminal 18, conductor 96 resistor 98, conductor 100, and to the negative terminal 102 of the D.C. supply 16.

When the resistor 68 is thus shunted by the switch 70, there will be a substantial increase in current through the resistor 98 by virtue of the characteristics of the Zener diodes 154 and 60, as compared with the change that would result if ordinary resistors had been used instead of Zener diodes. This is explained by the fact that these Zener diodes otter no opposition to increases in current ow ybeyond their voltage ratings. Thus a relatively large current differential is achieved by a small change in circuit resistance as compared with the total circuit resistance. An important advantage resides in the fact that such variables as relay resistance, line resistance, and other circuit parameters `are less critical when Zener diodes are employed in this fashion to produce the desired current differential. Moreover, the relay windings 58 and 90 are not overloaded by the increase in current required to produce the control function of the start-stop operation, since the current through the windings will remain constant, the increase occuring through the Zener diodes shunting them.

The increase in current through the resistor 98 increases the voltage drop across it to a value in excess of the rated voltage `of the Zener diode 146, producing a forward bias on the transistor 148, since current will now ow through the Zener diode 146 and the emitter-collector path of the transistor 148. This circuit can be traced from the positive terminal 80 of the D.C. source 16, conductor 82, resistor 84, conductor 86, contacts 132, Zener diode 136, conductor 162, winding 152, collector 150 and emitter 164 of transistor 148, conductor 166, conductor 100, and to the negative terminal 102 of the D.C. source 16. By completion of this circuit, the relay 144 will be energized, its contacts 168 closed, and the recorder 12 operated to receive dictation from the remote dictating station. When employing this circuit, the electrical and electromagnetic characteristics of the relay 144 are not critical, since the relay performs as a current sensitive device without requiring critical adjustment. This follows from the fact that any current in resistor 98 producing a voltage drop across it less than the rating of the Zener diode 146, say 6 volts, will not actuate the relay, whereas at any current in the resistor 98 that produces a voltage drop across it equal to or greater than the rating of the Zener diode 146, the relay 144 will operate.

While the invention has been described with reference to a single embodiment to serve as an example, variations that will lbe suggested to those skilled in the art are contemplated within the scope of the lappended claims.

I claim:

1. A control system comprising a voltage source, a relay winding, a resistor, and a control element, all connected in a series circuit, a Zener diode connected in parallel with said relay winding, and switching means connected across at least a portion of said resistor, whereby closure `of said switching means produces an increase in voltage across said control element without increasing the current in said' relay winding.

2. A control system `according to claim 1 including a second relay winding in said series circuit and a second Zener diode connected in parallel with said second relay winding.

3. A control system according to claim 1 including a second circuit containing a voltage source, a control relay winding, and a gating device in series, and' a Zener diode in parallel with said control element and in circuit with said gating device rendering said gating device conductive when the voltage across said control element exceeds the voltage rating of the last said Zener diode.

4. A control system according to claim 3 wherein said gating device is a transistor.

5. A control system according to claim 1 wherein said control element is a resistor.

6. A control system according to claim 1 wherein said relay winding operates contacts for energizing and deenergizing a recorder.

7. A control system according to claim 1 wherein said voltage source includes a plurality of Zener diodes arranged in series.

8. A control system according to claim 1 including a microphone in said series circuit.

9. A control system according to claim 1 including cathode and anode electrodes of a silicon controlled rectiiier in` said series circuit.

10. A control system Iaccording to claim 1 including contacts controlled by said relay winding in said series circuit.

References Cited UNITED STATES PATENTS 3,193,733 7/1965 Orsino S17-148.5 3,287,608 11/1966 Pokrant 317-142 3,293,495 12/1966 Smith 317-11 3,346,779 10/1967 Enk 317-1485 XR LEE T. HIX, Primary Examiner.

W. SHOOP, Assistant Examiner.

U.S. Cl. X.R. 317-1485 

1. A CONTROL SYSTEM COMPRISING A VOLTAGE SOURCE, A RELAY WINDING, A RESISTOR, AND A CONTROL ELEMENT, ALL CONNECTED IN A SERIES CIRCUIT, A ZENER DIODE CONNECTED IN PARALLEL WITH SAID RELAY WINDING, AND SWITCHING MEANS CONNECTED ACROSS AT LEAST A PORTION OF SAID RESISTOR, WHEREBY CLOSURE OF SAID SWITCHING MEANS PRODUCES AN INCREASE IN VOLTAGE ACROSS SAID CONTROL ELEMENT WITHOUT INCREASING THE CURRENT IN SAID RELAY WINDING. 